Outsoles for esd type protective footwear and methods of manufacturing the same

ABSTRACT

An outsole ( 2 ) for a footwear, which prevents electrostatic discharges (ESD) from a person wearing the footwear to a device being handled, is substantially made of a flexible material ( 5 ) and comprises an electrically conductive connection from an upper surface ( 2   a ) of the outsole to a lower surface ( 2   b ) of the outsole. The electrically conductive connection consists of one or several electrically conductive fibers ( 4 ).

FIELD OF THE INVENTION

The present invention relates to outsoles for footwear, which prevent electrostatic discharges (ESD) from persons wearing the footwear to devices being handled, and to methods for manufacturing such outsoles.

BACKGROUND OF THE INVENTION

Static electricity discharges from a person to an electrostatic sensitive device or material being handled, e.g. an integrated circuit or an electronic device, is often sufficient to damage the device. For example, it has been found that factory workers can generate electrostatic potentials in excess of 20,000 volts simply by walking on a factory floor. The friction between the sole of the footwear and the floor material causes a high voltage potential to develop on the worker. If the worker comes into close proximity to an electrostatic sensitive device, the charged worker can cause a discharge to the device and consequently damage it.

Various means have been attempted to provide electrostatic protection. The first such device is a dissipative strap which is placed around the user's ankle or in the shoe and which remains in contact with the heel, see e.g. U.S. Pat. No. 5,653,047. When the user generate an electrostatic potential by walking on a floor, the charge is substantially neutralized. Some of the problems with this device include user's failure to properly attach the device and failure of electrical component due to irregular walking, since the grounding device may not work properly until the heel comes into sufficient contact with the floor.

A second type of device is a static dissipative shoe. Typically, these shoes fall in the electrostatic discharge range of 10⁶ to 10⁹ ohms/sq. The outsole of such shoe has chemical substances blended with the plastic material of the outsole, to create a static dissipative resistance. Such shoe may have a limited use due to the relatively high resistance and further the chemical substance may limit the useful life of the device.

To overcome the above drawbacks U.S. Pat. No. 5,653,047 discloses a shoe comprising conductive plugs which are located in the toe region of the outsole of the shoe, and which protrude slightly above the upper surface of the outsole and below the lower surface of the outsole in order to provide stable contact with both the ground and a conductive layer on the inside of the shoe.

SUMMARY OF THE INVENTION

Problems and drawbacks associated with the shoe of U.S. Pat. No. 5,653,047 may include (i) complex and expensive manufacture, (ii) risk of occurrence of gaps or pockets between the conductive plugs and the outsole, in which dirt and moisture may be collected, (iii) inconveniences when using the shoe if the conductive plugs protrude too much and/or unreliable electric contact if the conductive plugs protrude too little, (iv) risk of unreliable operation after some time's use due to wearing down of the conductive plugs, and (v) a complicated structure at the upper end of the conductive plugs.

A main object of the present invention is therefore to provide an outsole for a footwear, which prevents electrostatic discharges (ESD) from a person wearing the to a device being handled, and by which be above problems and drawbacks of, the prior art can be avoided or at least alleviated.

A further object of the invention is to provide such an outsole, which has an improved reliability and resistance against wear and tear.

A still further object of the invention is to provide a method for manufacturing an outsole for a footwear, which prevents damaging of devices caused by electrostatic discharges, and which fulfils the above objects.

These objects, among others, are attained by outsoles and manufacturing methods as claimed in the appended patent claims.

The invention will be described in greater detail below with reference to the illustrative embodiments shown by way of example in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a shoe having an outsole in accordance with an embodiment of the present invention.

FIG. 2 is a cross sectional view of the shoe according to FIG. 1.

FIG. 3 is an enlarged part of FIG. 2.

FIGS. 4-6 are each a cross sectional view of a shoe having an outsole in accordance with an alternative embodiment of the invention.

Similar devices, parts, and details are denoted by similar reference numerals throughout the drawings.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2 show a shoe or footwear having an outsole in accordance with an embodiment of the invention. The shoe has an upper part 1 which is open at an upper end portion thereof and, if desired, can be provided with a protective cap (not explicitly shown) of conventional type. Reference numeral 2 indicates the outsole, and reference numeral 3 indicates an insole made of a comfort-improving material.

The outsole 2 comprises, according to the invention, an electrically conductive connection from an upper surface 2 a of the outsole to a lower surface 2 b of the outsole in the form of a plurality of electrically conductive fibers 4. The electrically conductive fibers may be of carbon, of a metal, of an electrically conductive polymer material, or of virtually any other kind of electrically conductive material.

The electrically conductive fibers 4 are preferably molded integrally in a hardenable flexible material 5, e.g. polyurethane material, of the outsole 2, so that the electrically conductive fibers 4 maintain the relative positions they adopt in connection with the molding process hereby, the electrically conductive fibers 4 are embedded in a hardenable binder, which at surrounds at least portions of the electrically conductive fibers 4, and, in a hardened state, fixates the electrically conductive fibers 4 in their positions relative one another.

According to the embodiment of FIGS. 1-3, the electrically conductive fibers 4 are arranged randomly in relation to one another in a non-woven condition, so that they do not form an arranged fibrous structure like a woven fabric or equivalent. The electrically conductive fibers 4 are preferably distributed directly in the mold in a random pattern.

The electrically conductive fibers 4 may be present throughout the entire outsole 2 or a major portion thereof, or they may be present at one or several separate lateral portions of the outsole 2. The length of the electrically conductive fibers 4 may be longer than a thickness of the outsole 2 of the shoe.

Preferably, the electrically conductive fibers 4 provide a plurality of electrically conductive paths from the upper surface 2 a of the outsole 2 to the lower surface 2 b of the outsole 2. Hereby, a more reliable low-resistivity electric connection is obtained.

With reference next to FIG. 4, which is a cross sectional view of a shoe, a further embodiment of the invention will be described. Here, each of the electrically conductive fibers 4 is fixated to the insole 3 (or to the upper surface 2 a of the outsole 2 or to any other layer in contact with the outsole 2) at a respective end thereof and the length of the electrically conductive fibers 4 are longer than the thickness of the outsole 2 of the shoe. The electrically conductive fibers 4 are arranged so that they each extend from the upper surface 2 a of the outsole 2 to the lower surface 2 b of the outsole 2 to thereby provide for multiple electric paths through the outsole.

FIG. 4 the electrically conductive fibers 4 are distributed evenly throughout the outsole to obtain a hair bristle brush like appearance of the electrically conductive fibers 4 even though the electrically conductive fibers 4 are embedded in the flexible material 5 of the outsole 2.

In FIG. 5 a similar embodiment is illustrated. Here, the electrically conductive fibers 4 are present at several separate lateral portions of the outsole 2.

In order to produce a manageable product made of such randomly oriented fibers the electrically conductive fibers 4 can be felted together. Felting means that the electrically conductive fibers 4 become hooked together and attached to one another in a non-woven condition. Such a felted or tangled layer can, even if it is thin, be handled as a unit during the procedure of manufacturing the outsole 2. Other methods of holding the fibers together which facilitate their handling can also be used.

In FIG. 6 an embodiment of the invention, which makes use of such felted layers in non-woven condition, is illustrated. The embodiment comprises a plurality of felted layers 4, wherein each layer comprises electrically conductive fibrous material that provide an electrically conductive connection from the upper surface 2 a of the outsole 2 to the lower surface of the outsole 2 b. The felted layers 4 are preferably arranged substantially vertically in the outsole 2 at multiple lateral locations of the outsole. Alternatively, only one felted layer comprising electrically conductive fibrous material is provided in the outsole 2.

Yet alternatively, or additionally, the plurality of electrically conductive fibers may include one or several woven layers of electrically conductive fibers in the outsole, possibly arranged vertically in the outsole.

Each of the felted or woven layers may be provided as a double, triple, or multilayer.

In an alternative embodiment the plurality of electrically conductive fibers may be stitched or knitted into a fiber based system, matrix, or layer made e.g. of a polymer material, which is then in turn molded integrally in the hardenable flexible material of the outsole.

The electrically conductive fibers 4 may comprise fibers of a linear density of fiber mass of between about 0.5 and about 5 denier, and/or fibers of different linear densities of fiber mass. The electrically conductive fibers 4 may be provided in lengths of between about 20 mm and about 100 mm.

The above outsole provides an excellent ESD protection function. A footwear with the above outsole will prevent electrostatic discharges from a person wearing the footwear to a device being handled. Further, the footwear reduces the risk for a person wearing the footwear of getting an electric shock due to an electrostatic discharge.

Besides, it has been noted that the resistance against wear and tear is strongly enhanced by the presence of fibers at the lower surface of the outsole.

Further, the outsole of the above kind may be provided with a flexible anti-nail protective layer arranged in between the insole 3 and the outsole 2 or within the outsole 2 as being described in our pending US patent application published under No. US-2006-0265909-A1.

The various embodiments of the outsole described above may be combined to form yet further embodiments of the invention. In particular, the plurality of electrically conductive fibers may be present in a plurality of the described structures or systems depicted above. Further, the embodiments may be manufactured in a plurality of manners according to the invention.

According to one method an outsole 2 for a shoe, which prevents damage caused by electrostatic discharges, is manufactured by (i) arranging or attaching electrically conductive fibers 4 at the under side of an insole 3 of the shoe, which in turn is attached to an upper part 1 of the shoe, and (ii) molding flexible material 5 to the insole 3 and optionally, to the upper part 1 to thereby fixate the electrically conductive fibers 4 in the flexible material 5 and thus form the outsole 2. Naturally, the electrically conductive fibers 4 have to extend through the entire outsole 2 to provide for an electrically conductive connection through the outsole. The electrically conductive fibers 4 may be arranged in any manner disclosed in the present description.

According to another slightly different method an out-role for a shoe, which prevents damage caused by electrostatic discharges, is manufactured by (i) arranging, or attaching electrically conductive fibers at the under side of an upper part of the shoe, which is closed at a lower end portion thereof, and (ii) molding flexible material to the upper part of the shoe to thereby fixate the electrically conductive fibers in the flexible material and thus form the outsole 2.

According to yet another method an outsole for a shoe, which prevents damage caused by electrostatic discharges, is manufactured, by (i) arranging electrically conductive fibers in a mold, and (ii) molding the outsole by feeding flexible material to the mold and harden the flexible material to thereby fixate the electrically conductive fibers in the flexible material of the outsole. The electrically conductive fibers are molded so that an electrically conductive connection from an upper surface of the outsole to a lower surface of the outsole is obtained. Preferably, electrically conductive fibers are protruding from the upper and the lower surfaces of the outsole. The outsole can in a later stage be attached to an upper part of a shoe, thus forming an entire shoe, which prevents electrostatic discharges from a person wearing the footwear to a device being handled.

It shall be appreciated that the term outsole as used in the present text covers outsoles of the type described above as well as any type of sole having a combined outsole and insole. 

1. An outsole for a footwear, which prevents electrostatic discharges from a person wearing the footwear to a device being handled, said outsole being substantially made of a flexible material and comprising an electrically conductive connection from an upper surface of said outsole to a lower surface of said outsole, wherein that said electrically conductive connection consists of one or several electrically conductive fibers.
 2. The outsole of claim 1 wherein said electrically conductive connection consists of a plurality of electrically conductive fibers.
 3. The outsole of claim 1 wherein said plurality of electrically conductive fibers provides a plurality of electrically conductive paths from the upper surface of said outsole to the lower surface of said outsole.
 4. The outsole of claim 2 wherein said plurality of electrically conductive fibers are present in a non-woven condition.
 5. The outsole of claim 4 wherein said plurality of electrically conductive fibers, which are present in the non-woven condition, are present throughout the entire outsole.
 6. The outsole of claim 4 wherein said plurality of electrically conductive fibers, which are present in the non-woven condition, are present at one or several separate lateral portions of the outsole.
 7. The outsole of claim 4 wherein said plurality of electrically conductive fibers, which are present in the non-woven condition, have each a length, which is longer than a thickness of said outsole, and wherein each of said plurality of electrically conductive fibers provides an electrically conductive path from the upper surface of said outsole to the lower surface of said outsole.
 8. The outsole of claim 6 wherein said plurality of electrically conductive fibers, which are present in the non-woven condition, are present as one or several felted layers.
 9. The outsole of claim 8 wherein said one or several felted layers are arranged substantially vertically in said outsole.
 10. The outsole of claim 2 wherein said plurality of electrically conductive fibers are present as one or several woven layers.
 11. The outsole of claim 10 wherein said one or several woven layers are arranged substantially vertically in said outsole.
 12. The outsole of claim 1 wherein said one or several electrically conductive fibers are molded integrally in said flexible material.
 13. The outsole of claim 1 wherein said one or several electrically conductive fibers are carbon fibers.
 14. The outsole of claim 1 wherein said electrically conductive connection comprises one or several electrically conductive fibers, which are stitched or knitted into a fiber based system, matrix, or layer.
 15. A footwear which prevents electrostatic discharges from a person wearing the footwear to a device being handled, said footwear comprising the outsole of claim
 1. 16. A method for manufacturing an outsole for a footwear, which prevents electrostatic discharges from a person wearing the footwear to a device being handled, the method comprising the steps of forming said outsole substantially of a flexible material; and forming an electrically conductive connection, which extends from an upper surface of said outsole to a lower surface of said outsole, wherein forming said electrically conductive connection by means of arranging one or several electrically conductive fibers in said flexible material.
 17. The method of claim 16 wherein said electrically conductive connection is formed by means of arranging a plurality of electrically conductive fibers in said flexible material.
 18. The method of claim 17 wherein said plurality of electrically conductive fibers are arranged in said flexible material in a non-woven condition.
 19. The method of claim 18 wherein said plurality of electrically conductive fibers, which are arranged in said flexible material in the non-woven condition, are distributed throughout the entire outsole.
 20. The method of claim 16 wherein said one or several electrically conductive fibers are stitched or knitted into a fiber based system, matrix, or layer, which in turn is arranged in said flexible material.
 21. The method of claim 16 wherein said one or several electrically conductive fibers are molded integrally in said flexible material.
 22. A method for manufacturing a footwear, which prevents electrostatic discharges from a person wearing the footwear to a device being handled, said method comprising the method of claim
 16. 